Remove data requirement from arc

[oscar-broman]

arc from d3-shape does not take any arguments: https://github.com/d3/d3-shape/blob/master/src/arc.js#L87

Fixes #886

[williaster]

From my comment in #886

I think data should be optional, not removed because it supports both types of usage.

arc optionally takes arguments as you can see in the readme and it's confusing but a few lines down from the line you linked you can see that arguments are passed along to the accessors.

Arc is functionally as it is used in the /chord demo. If you omit the data prop, it fails to draw anything. I think this is confusing because the d3 API supports two types of usage (and thus so does visx):

const arc1 = d3.arc();
arc1({ innerRadius, ... }); // "M0,-100A100,100,0,0,1,100,0L0,0Z"

const arc2 = d3.arc().innerRadius(...)...;
arc2(); // "M0,-100A100,100,0,0,1,100,0L0,0Z"

[williaster]

since data is already optional, I think this is probably the only line that needs to be removed since it is valid to call path without arguments.

[williaster]

This has been inactive for a while, closing in favor of #937